RANSAC homography on GPU

asked 2013-06-05 05:23:22 -0600

mada
105 ●2 ●7

updated 2013-06-05 05:34:19 -0600

Hello,

I couldn´t find an implementation of RANSAC algorithm on GPU in OpenCV, but only the CPU version - findFundamentalMat. When using low distance values, it takes a huge number of iterations to acquire desired confidence level and the execution time is increasing a lot. I am using it to make a better distinction between similar images(neighbor frames of video) and therefore lower distance values are desired.

My questions:

Will the algorithm be implemented for GPU in near future? Is it worth the time and possible speed-up to implement it by myself?

If anyone is familiar with some reliable GPU implementation of RANSAC outside of OpenCV, that could also be of use.

Thanks!

answered 2013-06-06 08:01:45 -0600

SR
1560 ●1 ●14 ●29

updated 2013-06-06 08:02:59 -0600

Apparently there is at least one GPU implementation for RANSAC but I haven't tried it. To be honest I doubt that it will be faster than a descent C/C++ implementation. I have implemented my own RANSAC variant (See [1] for details) and it has an enormous speed of about > 400 images/second including I/O (loading features and determining correspondences) by just using a single thread. Obviously using multi-threading will further increase the throughput. I am not familiar with GPU programming, but I guess RANSAC is not the kind of algorithm that perfectly suits the GPU programming paradigma.

[1] Stefan Romberg and Rainer Lienhart. Bundle Min-Hashing for Logo Recognition. ACM International Conference on Multimedia Retrieval 2013 (ICMR2013) [PDF]

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Why not perfectly suited? algorithm can be speeded up considerably by means of parallel computing, because the processing for each subsample can be done independently.

mrgloom ( 2013-06-07 03:08:33 -0600 )edit

I guess you mean the evaluation of the error function for each estimated homography. Yes, this may be done in parallel, but this just involves a simple matrix multiplication to project each sample by the estimate homography into the second image and is followed by a thresholding operation and finally the counting of inliers.

In my experience, the error function is not the bottleneck. I/O and determining the correspondences seem more expensive. Also, AFAIK I/O between CPU and GPU is expensive so I wonder if a GPU can really speed this up.

But I should add that I am telling this with my specific RANSAC variant in mind. It is based on 1-point-correspondences which make this process much simpler, faster and also more robust than e.g. a "classic" RANSAC variant like findHomography().

SR ( 2013-06-07 03:32:51 -0600 )edit

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